An all-fiber-based multiphoton endoscope will be developed for acquiring in vivo MPM signals from tissues. A femtosecond fiber laser and a small fiber probe will make it possible to detect MPM signals from small areas of internal cavities and organs. PolarOnyx proposes to develop an innovative high power femtosecond fiber laser with fiber delivering of undistorted femtosecond light pulses to tissues and a fiber bundle for collecting MPM signals excited from tissues. Using all-fiber-based components, the system will be compact, portable, and low-cost. In phase I, a femtosecond fiber laser will be developed and optimized for MPM applications. A miniature probe head will be designed to deliver excitation light and collect signals. Laser beam will be scanned in depth and multiphoton spectra will be acquired using a spectrograph. In phase II, the laser will be fully optimized and integrate with the fiber probe towards real clinic try. [unreadable] [unreadable] [unreadable]